1. Field of the Invention
The present invention relates to a silver halide photographic light-sensitive material, and more particularly to silver halide photographic light-sensitive material which excel in sensitivity and has its sensitivity little decreased after storage.
2. Description of the Related Art
In recent years, it has been increasingly demanded that the properties of silver halide photographic emulsions, in particular sensitivity, graininess, and sharpness, be improved to high levels. To meet the demand, it is proposed in, for example, U.S. Pat. Nos. 4,434,226 and 4,414,310, that tabular grains having an aspect ratio of 8 or more be used to improve the sensitivity-to-graininess ratio. To improve the sensitivity-to-graininess ratio by the use of tabular grains, it is important to allow a great amount of a sensitizing dye to be adsorbed by the grains according to the large surface area depended on the shape of each tabular grain, thereby to increase the light-absorption efficiency of the grains. Even if the light-absorption efficiency is increased, a sufficient amount of light may fail to reach an underlying emulsion layer. It followed that the sensitivity of the underling layer is impaired in some cases. In view of this, it is necessary to improve the latent-image forming efficiency, not the light-absorption efficiency, of the grain in order to increase the sensitivity of the emulsion.
The inventors thereof studied to see if the sensitivity of a silver halide emulsion can be increased by using regular silver halide grains, thereby enhancing the latent image forming efficiency, not the light-absorbing efficiency, of the silver halide emulsion.
Most spectral sensitizing dyes tend to deteriorate the latent image forming efficiency of a silver halide emulsion. (This efficiency is evaluated in terms of the number of photons each grain needs to absorb in order to form a latent image.) Hence, only in case that spectral sensitizing dyes are used in an amount far less than the amount required to form a continuous mono-molecular layer on the grain, suitable spectral sensitization can be achieved.
An emulsion hitherto known as effective to this problem is a so-called "internal latent image type emulsion" containing grains each having a ripening speck (hereinafter referred to as "sensitivity speck") which can form a latent image capable of being developed when the emulsion is exposed to light. U.S. Pat. No. 3,979,213, for example, teaches that the intrinsic desensitization occurred when an internal latent image type emulsion is spectral-sensitized is much less than that of an emulsion containing silver halide grains which have the same grain size and chemically sensitized in the surface only, and can therefore be effectively spectral-sensitized by using a great amount of a sensitizing dye. As is known in the art, such an emulsion has high storage stability since the sensitivity specks of the grains are not exposed out of the surface.
This type of an emulsion cannot be developed sufficiently, however, even it is processed with a developing solution designed for developing black-white color negative light-sensitive materials and color-reversal light-sensitive materials. After all, the sensitivity is not substantially sufficient. To solve this problem, it is proposed in JP-A-63-264740 and JP-A-1-302247, for example, that the distribution of the latent images be set at the maximum value in the very shallow region from the surface of each gain, thereby to increase the sensitivity and graininess of the emulsion. ("JP-A" means Published Unexamined Japanese Patent Application). If the latent image distribution is set at the maximum value in the shallow region from the surface of the grain, however, the internal latent image type emulsion can no longer have a sufficiently small intrinsic desensitization when it is spectral-sensitized. Thus, the sensitivity and graininess of the emulsion should better be improved further.
The inventors have found it possible to improve the sensitivity and graininess of an internal latent image type emulsion processed with an practically used developing solution, by introducing dislocation lines into the grains the emulsion contains.
Methods of observing dislocations within silver halide grains are described in many theses, among which are:
1. C. R. Berry, J. Appl Phys., 27, 636 (1956) PA0 2. C. R. Berry, D. C. Skilman, J. Appl. Phys., 35, 2165 (1964) PA0 3. J. F. Hamiltion, J. Phot. Sci. Eng., 11, 57 (1967) PA0 4. T. Shiozawa, J. Soc. Phot. Sci. Jap., 34, 16(1971) PA0 5. T. Shiozawa, J. Soc. Phot. Sci. Jap., 35, 213(1972)
These teach that the dislocations in crystals can be observed by means of X-ray diffraction method or transmission electron microscope method at low-temperature. Also do they disclose that various types of dislocations are generated in crystals when strain is applied, on purpose, to the crystals.
However, it is not that dislocations have been intentionally introduced into the silver halide grains described in these theses. Silver halide grains into which dislocations have been introduced on purpose are disclosed in JP-A-63-220238 and JP-A-1-201649. These publications teach that tabular silver halide grains having some dislocation lines introduced into them have better photographic properties, such as sensitivity and reciprocity law, than tabular grains having no dislocation lines. Also is it described in the theses that a light-sensitive material containing the tabular grains having dislocation lines excels i sharpness and graininess. However, tabular silver halide grains having dislocation lines and possessing satisfactory properties have yet to be available. Nor has any report been made on regular grains into which dislocations have been positively introduced.